1. Field of the Invention
The present invention relates to a micromechanical acceleration sensor having a substrate that has a reference electrode, and a seismic mass deflectable in a direction perpendicular to the substrate, a flexible stop being provided to limit the movement of the seismic mass.
2. Description of the Related Art
Modern sensors for measuring physical acceleration usually have a micromechanical structure made of silicon, also known as sensor core, and evaluation electronics. Sensor cores, which make it possible to measure an acceleration in a direction orthogonal to a main plane of the sensor core, are known as Z-sensors. Such sensors are used in the automotive sector, e.g., in ESP systems or perhaps in the field of wireless telephony. The sensor principle indicated is disclosed, inter alia, in published European patent document EP 0 244 581, which describes a micromechanical sensor for the automatic triggering of occupant-safety devices, and in published European patent document EP 0 773 443 B1, which shows a micromechanical acceleration sensor.
Typically, a micromechanical acceleration sensor includes a seismic mass deflectable in the Z-direction relative to a substrate, the seismic mass being joined to the substrate via a spring element. The maximum deflection of the seismic mass is limited by a stop device on the substrate. In the case of a stop of the seismic mass on rigid structures of the sensor, high force peaks may occur which must be processed by the micromechanical structure. This could result in mechanical damage to the structure.
Furthermore, because of the very small dimensions and spacings of the micromechanical structures, upon contact, the inter-atomic attractive forces may gain in importance as against the restoring force of the spring element to such an extent that the structure remains stuck in the limit-stop state. In order to minimize these disadvantageous effects, attempt has been made to construct the stop as a flexible stop via a relatively yielding, resilient connection.
Such a flexible stop in the Z-direction is already the subject matter of published European patent application document EP 2168809 A1 and published German patent application document DE 10 2008 043 753 A1. These designs have the disadvantage that the structures they propose have a relatively high space requirement, since the stop springs are realized in the thick functional layer of the micro-electro-mechanical system (MEMS) which has thicknesses greater than 10 μm, typically 15 μm to 20 μm. The great stiffness thereby caused must be offset by a correspondingly great length of the stop springs. This, in turn, is at the expense of precious space in the sensor core.